Coulomb's Law

Coulomb's Law

By Rachel Wampler

Point Charges:

• Point charge: an electric charge that exists at a single defined spot.

• ​Point charges exert force on each other

  • Force is related to the size of the charge and distance between them.

  • Same types of charge force repulsion

  • Opposite charges force attraction​

• ​The force of the first point charge to the second point charge is equal and opposite to that of the second point charge to the first point charge

  • Newton's Third Law​

Coulomb's Law

• The electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects.

• Where:

  • F - electrostatic force

  • k - ​Coulomb's Constant (8.99 x 10⁹ Nm²/C²)

  • q - Charge

  • r - Distance between charges​

Multiple Choice

In a hydrogen atom, the electron (q = -1.60 x 10^-19 C) is 5.29 x 10^-11 m away from the proton of equal charge magnitude. Find the electrical force of attraction.

• 8.99 x 10⁹ N

• 8.22 x 10^-8 N

• 0 N

• 8.99 x 10^-9 N

Inverse Square Law

Multiple Point Charges

• Force on 1 point charge by 2 other point charges

• ​Work in two parts

  1. ​Find the attraction forces

     1. ​Find force of attraction by one of the points

     2. Find force ​ of attraction by the other point

  2. Add the ​force vectors

• REMEMBER: ​There may be x and y components!!!

​

Multiple Choice

There are three charges in a straight line:

$$q_1=\ +2\mu C\ at\ x=-0.1m$$  

$$q_2=\ -3\mu C\ at\ x=\ 0m$$  

$$q_3=\ +5\mu C\ at\ x=0.3m$$  

What is the force on q₂?

• +3.89 N

• +5.39 N

• -5.39 N

• -3.89 N

Multiple Choice

There are three charges:

$$q_1=\ +2\mu C\ at\ \left(0,0.3\right)m$$  

$$q_2=\ -3\mu C\ at\ \left(0,0\right)m$$  

$$q_3=\ +5\mu C\ at\ \left(0.1,0.2\right)m$$  

What is the force on q₂?

• 3.247 N @ 68.1 ^o above the horizontal

• -2.414 N @ 63.4 ^o above the horizontal

• -3.247 N @ 68.1 ^o above the horizontal

• 2.414 N @ 63.4 ^o above the horizontal